In nearly every episode, Gus, Lauren and Peter use some kind of gun to fire at the weekly villain--here, it's a shotgun that fires balls of dirt.
Evil Shirley's weakness is mud because the villain is based on Lauren's mother and Lauren's mother is a compulsive neat-freak.
The "Evil Shirley" villain shoots icicles and freezes her victims solid as she is an "Ice Queen." She seems intent on destroying love.
Evil Shirley's other weakness is if a house falls on her. She is defeated when a motor home runs over her.